The known tempering devices of the type mentioned above are built and dimensioned to obtain "optimum" tempering of the chocolate-like mass at nominal capacity, i.e. at a predetermined chocolate flow.
Large amounts of constantly flowing cooling and heating medium circulate in the separate cooling and heating circuits of the devices under stable operating conditions. Thus, the circulating cooling and heating medium amount is adapted to discharge and supply the necessary heat energy amount from and to the chocolate mass to achieve the desired temperature and thus presumed optimum state of the chocolate mass at a nominal capacity.
In other words, at the nominal capacity of the tempering apparatus the operation is optimum because the area of the cooling and heating surfaces is correct for the nominal chocolate flow. In other words, the heat energy discharge from or supply to the chocolate mass is optimum.
Therefore, the efforts have always been focussed on controlled regulation of the temperature of the cooling and heating medium for the circulation circuit concerned on the basis of the measured mass temperature at the outlet of the zone which is associated with the circulation circuit concerned.
When the known chocolate tempering devices are to work at a capacity which is not nominal, e.g. 50% of it, it is difficult to obtain optimum control of the apparatus and thus the desired state of the tempered chocolate mass, without having to perform manual control operations on the apparatus in operation. The reason is that the extent of the cooling and heating surfaces is much too great with respect to the flow of the chocolate mass, and the transport of heat energy to and from the chocolate mass is therefore difficult to control to the desired level.
In particular, it has been found difficult to control the heat energy transport in the crystal formation area of the apparatus, which is particularly critical because precisely the control of this area is of decisive importance for the state of the finish-tempered chocolate mass.
The state of the finish-tempered chocolate mass is predominantly determined by its final temperature and content of stable beta crystals. The desired final temperature is determined on the basis of preceding tests and empirical values of the composition of the constituent parts, such as the fat content, of the chocolate mass concerned. The content of stable beta crystals should always be around 5% when subsequent high quality characteristics of the moulded chocolate article are to be obtained, such as long shelf life, uniform appearance without dullness, good taste, etc., as is known in the chocolate making industry. The desired content of the stable beta crystals in the tempered chocolate mass can fluctuate slightly around the 5%, depending upon whether the chocolate mass is subsequently to be moulded or used for coating articles.
When the known tempering devices work at a lower capacity than the nominal one, at which they are designed to operate optimally, there will be an excessive cooling surface area (a too large cold spot) in the crystal formation area when, other things being equal, the temperature is the same as at the nominal capacity. There will hereby be an excessive heat energy transport from the chocolate mass, and too many crystals will undesirably be formed in it.
The only possibility of obtaining a better control is to raise the cooling water temperature, so that the heat energy transport from the chocolate mass is reduced. When the cooling water temperature is regulated in response to the measured chocolate temperature at the crystal formation area, the cooling water temperature will be increased automatically when the chocolate temperature decreases, which will be a consequence of an excessive heat energy transport away from it.
However, the formation of the most important beta crystals will not be initiated until the chocolate mass has been cooled to a predetermined temperature level, which, in the known tempering devices, has been found to correspond to a temperature of the cooling medium (cooling water) of about 16.degree. C. Therefore, if the temperature of the cooling medium is too high, which is frequently the case with the controlled regulation in the known chocolate tempering devices, the crystal formation will not begin at all. It has therefore been found that it is difficult for the known chocolate tempering devices to work reliably in operation to achieve the desired content of stable beta crystals in the tempered chocolate mass, when working with a considerably lower capacity than the nominal capacity, e.g. about 50% of the nominal capacity.
EP-O 472 886 A1 discloses a method and a tempering device in which the flow amount and/or temperature of the cooling medium in one or more of the initial zones is controlled by means of a control unit which measures the temperature of the chocolate mass at the end of the crystal formation area. However, the control is a kind of feedback control which, as found by a skilled person, has a very long reaction time before "equilibrium" is obtained again and the desired temperature of the chocolate mass has been reached before it passes into the crystal formation area. The document only contains teachings with respect to maintaining a constant cooling medium temperature at the crystal formation area. The document provides no teachings on how to achieve a separately controlled regulation of the heat energy transport in the crystal formation zone which is very important for the beta crystal formation.